1. Field of the Invention
The invention relates to a trailing arm suspension. In one of its aspects, the invention relates to a trailing arm suspension having a beam that utilizes a shrink fit to secure the spring beam to an axle without welding.
2. Description of the Related Art
Trailing arm suspensions are well known and commonly used in heavy-duty applications such as a tractor-trailer configuration. The trailing arm suspension typically comprises a pair of spaced trailing arm assemblies mounted to opposite sides of the vehicle, with each trailing arm assembly carrying an axle supporting the vehicle wheels.
The trailing arm assembly comprises a trailing arm having one portion pivotally mounted to a hanger bracket that depends from a vehicle frame rail. An air spring is disposed between another portion of the trailing arm and the vehicle frame rail to dampen the rotation of the trailing arm relative to the vehicle frame.
An important function of the trailing arm suspension is compliance in response to vehicle roll-induced forces. The vehicle roll-induced forces are typically created during the turning of the vehicle. As the vehicle is turned, the vehicle tends to rotate about its longitudinal axis in response to the G-forces encountered during the turn, causing one side of the vehicle to drop and another side of the vehicle to rise. This relative movement results in a corresponding relative rotational movement between the trailing arms on opposite sides of the vehicle. The suspension must be sufficiently compliant to permit some rolling of the vehicle in order to avoid undue torsional stress on the axles. However, the suspension must also be sufficiently stiff to resist vehicle roll beyond a predetermined roll angle for safety reasons. Generally, it is desirable to limit vehicle roll to a roll angle of about 2½ degrees for most trailing arm suspensions. The roll angle is the arc traversed by trailer about its longitudinal axis measured relative to a horizontal line passing through the center of gravity of the vehicle.
In rigid beam trailing arm suspensions, the roll stiffness of the suspension is achieved through the mechanical torquing of the axle as the rigid trailing arms move relative to each other to twist or torque the axle. If the mechanical torquing of the axle is too great, it can cause premature failure of the axle. The suspensions are made compliant to the roll with the use of a resilient connection between either or both the pivotal connection of the trailing arms to the hanger bracket and the connection of the axle to the trailing arm. The resilient connections are typically achieved by elastomeric bushings.
An ideal trailing arm suspension is substantially compliant up through about 2½ degrees of roll angle and then quickly becomes stiff to prevent the vehicle from rolling through too great of a roll angle. In other words, on a plot of roll moment versus roll angle, an ideal suspension will have a generally linear relationship between the roll moment and roll force until the compliance is exceeded then the curve will tend toward being infinite.
An alternative to the rigid beam trailing arm is a flexible beam also known as a spring beam. A spring beam typically is manufactured from spring steel that is capable of flexing in the vertical direction in response to vertical forces. One end of the spring beam is mounted to a hanger bracket by either a pinned connection or a resilient connection in the nature of an elastomeric bushing. The other end of the spring beam is rigidly mounted to the axle, usually through a bolted connection with an axle bracket that is welded to the axle, thus eliminating the need for a resilient connection between the axle and the beam. The spring beam advantageously functions much like a spring in that the response is relatively linear.
Typically, the axles must be made of sufficient thickness so that the torsional resistance of the axle at the welded joint is sufficient to meet torsional requirements for the suspension. On the other hand, non-welded axle connections can have thinner wall thickness and thus less weight and cost for the same suspension rating. Trailing arm suspensions with non-welded axle connections are disclosed in WO 97/06022, published Feb. 20, 1997, and U.S. Pat. No. 6,805,369.